The present invention relates to a method and apparatus for continuous casting of metal sheet whose section dimensions, especially width, can be held within very close tolerances.
Continuous casting has been used to produce sheets of silicon steel, hard-to-machinable heat-resisting alloys for jet engines, aluminum foil and the like. In FIG. 1 is shown a prior art continuous casting process using a pair of rolls a in which cooling water flows. Molten metal c is supplied through a nozzle b and metal sheet d is cast by the pair of rolls a.
Molten metal c fed to a wedge-like space defined by upper portions of the rolls a is cooled and solidified by the rolls a and is continuously drawn downwardly.
However, as shown in FIG. 2, immediately after the pouring of molten metal c, the width of solidified metal sheet d is gradually shrinked. That is, the cast metal sheet d has a width which is substantially narrower than the width of molten metal c poured between the pair of rolls a. For instance, assume that the temperature of molten metal is 1,500.degree. C.; the thickness of cast metal sheet is 0.15 mm; and the peripheral velocity of the pair of rolls a is 15 m/sec. Then, if the width W.sub.1 of the poured molten metal; that is, the width of a mold is 100 mm, then the cast metal sheet d shrinks over the length l.apprxeq.20 m so that the width W.sub.2 of the finished product becomes about 50 mm (See FIG. 2).
As described above, the width of the finished product is narrower than the casting width so that the yield is poor and the desired correct edges cannot be obtained. In addition, splashes adhere to the surfaces of the finished product so that the quality of the finished product is degraded. Thus it has been difficult to practically employ the continuous casting methods and machines of the type described above.
The inventors made extensive studies and experiments in order to overcome the defects encountered in the prior art continuous casting methods and machines and found out that upon pouring of molten metal the gap between the rolls a is uniform over the whole length thereof so that molten metal is sufficiently cooled and solidified over the whole length of the rolls a, but after pouring heat crowns appear over the cylindrical surfaces of the rolls a as shown in FIG. 4 and consequently the gap or distance between the rolls a is increased at the edge portions thereof. As a result, molten metal poured adjacent to the edges portions of the rolls a is not solidified and is scattered. Moreover, the longer the teeming or pouring operation, the more pronounced the degree of heat crown is so that unsolidified portions e are increased and consequently the width W of the solidified metal is decreased. After the degree of heat crown has reached its maximum, further shrinkage of the solidified width W is stopped. It was further found out that because of splashing from the edge portions or unsolidified portions e, the edges of the resulting product cannot be correctly finished. In addition, splashes from the unsolidified portions e adhere to the product d.
In view of the above, the primary object of the present invention is to provide a novel method and apparatus for continuous casting of metal sheet, whereby no heat crown is produced over the cylindrical surfaces of casting rolls so that no unsolidified portions are produced and consequently the resulting product may have a predetermined width, the edges of the product can be correctly finished and the adhesion of splashes over the surfaces of the product can be eliminated.
The above and other objects, effects and features of the present invention will become more apparent from the following description of a preferred embodiment thereof taken in conjunction with the accompanying drawings.